1. Field of the Invention
The invention relates to a method of initializing a pluggable electrical unit in a modular system.
2. Description of the Prior Art
Complex electrical engineering systems, in particular in measuring and control technology and in telecommunications, are often of a modular construction. This involves a large number of electrical units being accommodated in an enclosure of an electrical base unit in a pluggable manner. The pluggable electrical units are mechanically of an identical construction but electrically different according to their intended function.
When a complex system of this type is expanded by adding further pluggable electrical units while operation is in progress or when one of the pluggable electrical units is exchanged, there is the risk of electrical components of the pluggable electrical unit and/or of the base unit being damaged or destroyed if an electrical unit which, though mechanically able to be inserted into the slot, is not electrically and functionally intended for this slot is inserted into the slot. Even in the case of mechanically and electrically fitting pluggable electrical units, disruptions to units already in operation and damage to the unit to be inserted occur during insertion as a result of capacitive charging or discharging currents.
DE 196 10 556 discloses a bus access unit for connecting a subassembly of a programmable controller to a bus, which subassembly is spatially arranged in the base unit and is tested by means of a test contact and an evaluation circuit to ascertain that it is a plug-in module and, if it is a plug-in module, a variable resistor fitted into the feed line of the plug-in module is switched to low resistance after a predetermined waiting time. The variable resistor is switched to high resistance again when the potential at a test contact lies outside a predetermined value range after a predetermined stabilizing time.
EP 798 647 discloses an arrangement for the connection of a device to a line system in which the communication bus is reset each time a new device is inserted in order to avoid disruptions on the bus. It is disadvantageous in this case that the communication is temporarily suspended in the entire system.
Furthermore, EP 888 589 discloses a connecting method for connecting a subassembly of a programmable controller to a bus, in which firstly the power supply of the subassembly is connected in a ramp-shaped manner. Subsequently, the communication lines are switched unidirectionally to low resistance in such a way that transmission activities of the subassembly are prevented. Only when the subassembly re-sends an acceptance signal after successful evaluation of the bus traffic are the communication lines switched bidirectionally to low resistance.
All the known connecting methods require that the electrical interface of the plug-in module and that of the base unit coincide. Such uniform interfaces no longer allow individualizing of the electrical interface of the pluggable electrical units that is designed for the plug-in contact device, since plug-in contacts of the same name would be wired to different types of signals, which may also differ in the direction of signal transmission. If the free choice of slots is maintained for all the pluggable electrical units, the number of necessary plug-in contacts increases in proportion to the degree of individualization of the pluggable electrical units, and so does the complexity of the backplane wiring and of the bus access units. This additional complexity is felt to be disadvantageous. In addition, the overall size of the plug-in connector increases with the number of pins. Plug-in connectors of a larger overall size are at odds with the miniaturization of pluggable electrical units.
The invention is therefore based on the object of specifying a method of initializing a pluggable electrical unit in a modular system which is suitable for taking into account electrical interfaces of different types for electrically and functionally different plug-in modules while maintaining the free choice of slots in such a way that disruptions to units already in operation and damage to the unit to be inserted are avoided.
The invention is based on a modular system comprising a base unit and at least one pluggable electrical unit, each pluggable electrical unit having module electronics and a read-only memory with clearly identifying identifiers. The interface between the base unit and the pluggable electrical unit is provided with a variable resistor, arranged in a feed line, first switching means, via which the read-only memory is disconnected from the base unit, and second switching means, via which the module electronics are disconnected from the base unit.
The essence of the invention is to establish the connection between the base unit and the pluggable electrical unit initially only partially, and only to the read-only memory, after switching on the power supply to the pluggable electrical unit. After that, the pluggable electrical unit is identified and, in accordance with the identity of the pluggable electrical unit, the full connection or full isolation between the base unit and the pluggable electrical unit is established.
This reliably avoids any disruption being caused to other units already in operation by differently configured signal lines for the connection of the pluggable electrical unit to the base unit.
To be specific, in a first step the variable resistor is brought into its low-resistance state in a controlled ramp-shaped manner after the elapse of a first waiting time, which begins with the insertion of the pluggable electrical unit.
In a second step, the first switching means are switched to conduct and the read-only memory is connected to the base unit after the elapse of a second waiting time, beginning with the end of the first waiting time.
The identifying identifiers are read from the read-only memory. On the basis of the identifying identifiers, the compatibility of the pluggable electrical unit with the base unit is tested.
If it is compatible, the interface of the base unit is configured in accordance with the identifying identifiers, the second switching means are switched to conduct and the module electronics are connected to the base unit. This fully connects the pluggable electrical unit electrically to the base unit.
If it is incompatible, the read-only memory is disconnected from the base unit and the variable resistor is brought in a controlled manner into its high-resistance state. This fully isolates the pluggable electrical unit from the base unit. Consequently, disruptions to units already in operation and damage to the pluggable electrical unit are reliably avoided.